1. Field of the Invention
The present invention relates to a novel process for preparing alkylene or dialkyl ketals of alpha-acetyl cinnamic acids or esters thereof by reacting an alpha-acetyl cinnamic acid or ester thereof with a ketalizing agent in the presence of a transition metal catalyst and an acid catalyst. This invention also relates to a process for producing aliphatic alpha-enol ethers of alpha-acetyl cinnamic acids or esters thereof.
The ketals and alpha-enol ethers produced by the processes of the invention can be used directly to synthesize naphthanoic acids or esters thereof.
2. Description of the Background
Substituted ketals, alpha-enol ethers or alpha-enol esters of alpha-acetyl cinnamic acids or esters thereof are useful for the synthesis of substituted 2-naphthanoic acids and esters thereof which are polymer intermediates. In order for 2-naphthanoic acid derivatives to be useful polymer intermediates a second functional group besides the carboxyl group must be present on the aromatic ring. Moreover, such functional group must be present at a specific location on the molecule. Consequently, it is important tht the alkylene and dialkyl ketones and alkyl alpha-enol ethers of alpha-acetyl cinnamic acids or esters thereof from which the 2-naphthanoic acid derivatives are obtained be substituted at specific sites on the aromatic ring. The development of such a process is of great significance to the industry.
A number of general methods for the ketalization of ketones are known (Gasparrini, F., Giovannoli, M., and Misiti, D., Tetrahedron 40: 1491 (1984) and references cited therein). These methods include the synthesis of ethylene and dimethyl ketals from alpha-beta unsaturated ketones. These methods, however, utilize no transition metal catalysts. Moreover, no known applications of these methods to alpha-acetyl cinnamic acids or esters thereof are known.
Accordingly, there is still a need for a general process for the synthesis in good yield of alkylene and dialkyl ketals and alpha-enol ethers of alpha-acetyl cinnamic acids and esters thereof having a predictable substitution pattern and good yield.